Semiconductor processing often involves the deposition of films or layers over or on a semiconductor substrate surface which may or may not have other layers formed thereon. For example, during integrated circuit fabrication, thin films of dielectrics, polysilicon, and metal conductors are deposited on the wafer surface to form devices and circuits. Exemplary techniques used for forming these thin films are physical vapor deposition (PVD), chemical vapor deposition (CVD), and epitaxy (a special case of CVD). As an example, CVD involves a chemical reaction of vapor phase chemicals and reactants that contain the desired constituents to be deposited on the substrate or substrate surface. Reactant gases are introduced into a reaction chamber or a reactor and are decomposed and reacted at a heated surface to form the desired film or layer.
Semiconductor processing is typically carried out under a controlled environment, with particulars of the environment depending on the process being implemented. For example, there are three major CVD processes which exist and which may be utilized to form the desired films or layers on a substrate surface. These are: atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), and plasma enhanced CVD (PECVD). The former two processes (APCVD and LPCVD) are characterized by the pressure regimes and typically use thermal energy as the energy input to effect desired chemical reactions. The latter process (PECVD) is characterized by its pressure regime and the method of energy input.
Irrespective of the semiconductor process being used, it is further desirable to reduce the amount of particles and airborne contaminants present within a semiconductor processing chamber in order to realize a clean environment. Such a clean environment minimizes device defects, increases yields, and decreases the overall costs when fabricating integrated circuits. For the case of CVD systems, reaction chambers formed from quartz or stainless steel contain wafer holders formed from graphite, quartz or stainless steel. The substrate, or wafer holder, in one construction is directly heated by induction irradiation, with the reaction chamber walls remaining cold. Such a system is often described as a cold wall system. As such, the reaction takes place right at the wafer surface and is usually cleaner because the film does not build up on the chamber walls. With one such cold wall deposition system, precursors are used that are volatile enough to supply a sufficient amount of vaporized precursor to the process chamber. In this case, the gas lines and chamber walls do not need to be heated. However, particle contamination still remains a problem.
Alternatively, there exists a hot wall deposition system wherein the reaction takes place in the gas stream and the reaction product is deposited on surfaces of the system, including the reaction chamber walls. With one such hot wall deposition system, the reaction takes place at, or above, the wafer surface. Some precursors that are used are not very volatile and must be heated to supply enough vaporized precursor to the process chamber. Since the vaporized precursor will condense on any unheated surface, gas lines and chamber walls must be heated. The temperature where the reaction occurs is higher than the gas lines and chamber walls, but there are still unwanted deposits on the chamber walls, wafer holder and shower head. Such unwanted depositions can build up and flake off from the surfaces over time. Unless the reaction chamber is properly cleaned and maintained, the surfaces become a source of contamination during processing. A particular concern occurs when implementing wafer processing within a vacuum, or sub-pressurized atmosphere, wherein wafers are transferred into and out of the wafer processing chamber such that rapid pressure changes occur each time the transfer chamber is opened and closed. Such pressure changes can further result in dislodgement of deposits which have built up on inner wall surfaces of the reaction chamber, as well as on the semiconductor processing chamber.
Furthermore, other types of semiconductor wafer processors such as diffusion and oxidation furnaces must also maintain a clean internal environment. Irrespective of the source of particle contamination, whether from contaminants found in processing gases or from deposition and subsequent dislodgement of reaction product on inner surfaces of the system, there is also a need to minimize contamination so as to provide for low contamination levels and a clean environment when implementing any form of semiconductor wafer processing.
This invention grew out of concerns associated with improving the containment of particulate contaminants within semiconductor wafer processors and methods. This invention also grew out of concerns associated with improving the advantages and characteristics associated with reaction chambers of semiconductor wafer processors, including those advantages and characteristics mentioned above.